French Patent Application No 9214680, filed on Nov. 26, 1992 in the name of the Applicant, describes a method and installation for monitoring, continuously and in real time, a complex manufacturing process.
FIG. 1, to which reference is now made, shows diagrammatically a monitoring installation as described in the patent application mentioned above. The purpose of this installation is to monitor continuously a complex manufacturing process. The manufacturing process is implemented by a machine in order to convert a raw material into a finished product. In order to be able to monitor the manufacturing process, sensors are disposed which monitor the machine and the product at any stage in its conversion. The arrangement and nature of each of the sensors are chosen so as to be able to monitor a basic element of the manufacturing process. Thus sensors are used for temperature, pressure, tension, vibration, illumination, thickness, speed, flow rate, electrical charges, potential, optical density or viscosity, as well as any other type of sensor useful for monitoring one of the basic elements of the manufacturing process.
Each sensor forms part of a channel C.sub.1, C.sub.2, . . . , C.sub.n, . . . Each channel sends a signal to a network 10, in a manner which is well known in the art. This signal then reaches monitors 12a, 12b, 12c.
The network 10 can be any type of local area network such as for example FILBUS, described notably in Control Engineering of October 1987, or in Minis et Micros No 313 of 19 Dec. 1988. The network may also be the FIP network described in the draft standards NF C46-601 to NF C46-607. An FIP network was used, formed by a shielded twisted pair operating at 2.5 MHz, but it is obvious that the information could be passed just as well over optical fibres at 5 MHz as recommended by FIP in a particular embodiment.
The monitors 12a, 12, 12c are equipped with suitable cards, for example an FIP coupler card (CC 105 made by Cegelec.RTM.), so as to be connected to the network 10 in order to receive the information supplied by the set of channels C.sub.1, C.sub.2, . . . C.sub.n, . . . Advantageously, the monitors 12a and 12c may take the form of microcomputers of the PC 486 type or similar. In particular it makes it possible to analyse the information received and to correlate the information coming from the different sensors. The monitor 12b also may consist of a microcomputer of the PC 486 type or similar.
Advantageously, this monitor makes it possible to feed a data base 14 for collecting information relating to the manufacturing process and to build up a history for the purpose of subsequent use in order to study any slow or cyclic drifts as a function of external parameters. It is obvious that, in order to be able to produce correlations between the signals coming from the different sensors or to build up a history which can be used subsequently, each spectrum or signal must be accompanied by a synchronisation signal coming for example from a single clock internal to the system. The monitors automatically determine the time taken by the product to pass from one given sensor to another sensor as a function of the speed of movement of the product, which can be measured by other sensors. The monitor 12b can be equipped with a network card of the IEEE 802 type so as to be able to interrogate the data base in non real time through a network 16, by means of a remote workstation 18, which may be a DEC.RTM. station operating in WINDOWS.RTM..
As shown in FIG. 1, the network 10 is also connected to actuators A.sub.1, A.sub.2, . . . A.sub.p, which enable control means of the machine to be used. The monitor 12c communicates with the monitor 12a and may comprise an expert system for using, on receipt of information coming from the monitor 12a, the appropriate actuators.
The actuators Ai have a structure similar to the channels Ci in which the sensors 20 are replaced with motors or the like, often referred to as actuators in the art. Each actuator transmits the instructions from the network 10 to a motor, for example, passing through the processor 28.
The mode of functioning of the actuators is considered as the inverse of the mode of functioning of the acquisition channels and is characterised in that the objective parameters supplied by the monitor 12c are used by any inverse spectral analysis means (inverse FFT, for example, or any other algorithm such as digital filter, adaptative commands and real time identification of the process), with precise control of the phase (in order to avoid any hunting phenomenon) so as to generate an analogue signal, the spectral components of which tend to minimise the frequencies disturbing the product.
FIG. 2, to which reference is now made, illustrates diagrammatically one of the monitoring channels, as used in the application mentioned above.
As mentioned before, a sensor 20 is used in order to convert the physical phenomenon to be monitored into an analogue electrical signal. The sensor 20 is associated with conditioners 21 which make it possible to provide a signal of relatively high amplitude lying for example between .+-.100 mV and .+-.10 V, so as to be able to reach the analogue to digital converter situated a short distance away (approximately one meter maximum) without being affected to any great extent.
As can be seen in FIG. 2, the signal coming from the sensor is sent to a circuit 22 converting the analogue signal from the sensor 20 into a digital signal. In order to limit any noise which might occur on the connection between the sensor 20 and the circuit 22, the analogue to digital circuit is disposed as close as possible to the sensor 20. The parameters influencing the measurement are also supplied to the converter so as to be able to take account of influences external to the sensor on the measurement performed by the sensor 20. The circuit 22 comprises an anti-aliasing filter in order to meet the Shannon conditions relating to sampling, and a converter 24 which supplies a digital output signal which is a function of the amplitude of the analogue input signal.
The digitised signal is then sent to a circuit 25 and stored therein in a RAM 26 under the control of a microprocessor. Because of the particular utilisation envisaged, the microprocessor used is a DSP 56001 manufactured by MOTOROLA.RTM.. Acquisition of the signal takes place in real time. Advantageously, the memory 26 is a circular memory which can be obtained by means of a pointer involving a modulo function.
As can be seen clearly in FIG. 2, the processing module 25 and the conversion module 22 are located in the same physical entity. In reality, the unit 25 is connected to the unit 22 by means of a data bus. This entails the production of an interface card specific to each sensor used. This substantially increases the cost and complexity of the installation with regard to each of the sensors or actuators. In addition, since these cards are specific to each sensor or actuator, they must be produced one by one "to measure" according essentially to the envisaged application.
Another problem related to this approach lies in the fact that the acquisition, conversion and processing elements must be located geographically at the same place, only the monitoring devices being remote because of the use of the local area network 10.
Finally, the connection between the conversion module and the processing module 25 is liable to be disturbed by parasitics detrimental to the quality and reliability of the control and monitoring carried out.